Proposed work includes iron metabolism, red cell metabolism and kinetics, and granulocyte kinetics. Studies of iron metabolism are concerned with isotopic and biochemical measurements in animals and man of iron absorption, internal iron exchange, tissue handling of iron and its regulation, and pathophysiologic aspects of iron deficiency and iron overload. Erythrocyte metabolism will be studied in cells incubated in vitro at 37 degrees C. Erythron kinetics will be further developed as a measure of red cell production and applied to specific clinical problems, including aplastic anemia, thalassemia, and sickle cell anemia. Granulocyte kinetics will be examined in animal models and in clinical disorders.